I've got this problem when using the selection buffer. I've got a program set up so that you can click your mouse, drag it, and the area you selected is used for the gluPickMatrix. It works fine when there are just a few objects within the selected area, but when lots of objects are in the area (100+, I don't know exactly when problems start) I get problems.

When lots of objects are within the region my canvas displays the gluPickMatrix and nothing gets selected. Its as if the pickObjects method is getting interrupted by the display method before it is finished.